Field of the Invention
The present invention relates to an electrophotographic photoconductor, a process cartridge including an electrophotographic photoconductor, and an electrophotographic apparatus including an electrophotographic photoconductor.
Description of the Related Art
Presently, the oscillation wavelength of semiconductor lasers commonly used as the device for image exposure in the field of electrophotography is as long as about 650 to 820 nm, and development of electrophotographic photoconductors that have high sensitivity for such long-wavelength light has been pursued. Also pursued is the development of electrophotographic photoconductors that have high sensitivity for light of semiconductor lasers whose oscillation wavelength is short in order to further increase image resolution.
Phthalocyanine pigments are known to serve as charge-generation substances that have high sensitivity for light from such a long-wavelength range to such a short-wavelength range. In particular, oxytitanium phthalocyanine and gallium phthalocyanine have excellent sensitivity properties and various crystal forms have been reported to date.
However, electrophotographic photoconductors that use gallium phthalocyanine pigments generate a large number of photocarriers (holes and electrons) and thus electrons that pair with holes that have migrated through the hole transport substances tend to remain in photosensitive layers (charge generation layers). Thus, electrophotographic photoconductors that use gallium phthalocyanine pigments frequently encounter a phenomenon known as ghosting. Specifically, positive ghosting in which only the portions irradiated with light in the previous run appear dense and negative ghosting in which only the portions irradiated with light in the previous run appear sparse are observed in output images.
Japanese Patent Laid-Open No. 2012-32781 reports that ghosting can be addressed by adding a particular amine compound to a charge generation layer.
In order to withdraw electrons from a charge generation layer and reduce charge injection from a support to a photosensitive layer side, an electron transport substance has been added to an undercoat layer or an intermediate layer so that this layer functions as an electron transport layer. The undercoat layer containing an electron transport substance has a higher resistance than the undercoat layer that uses conductive ions or metal oxide fine particles and strongly reduces charge injection from the support side to the photosensitive layer side.
Japanese Patent Laid-Open No. 2010-145506 discloses an undercoat layer (electron transport layer) solely composed of a binder resin and a tetracarboxylic acid imide compound serving as an electron transport substance. The undercoat layer exhibits high mobility and significantly reduces charge injection. However, since the electron transport substance is solvent-soluble, the electron transport substance may leach out into a photosensitive layer or a coating liquid if a photosensitive layer is formed on the undercoat layer by coating, in particular, by dip-coating. As a result, the inherent electron transport ability is not fully exhibited and the electron transport ability has been insufficient in some cases. The electron transport substance leaching into the photosensitive layer (charge generation layer) degrades inherent electrophotographic properties of the photosensitive layer, such as chargeability, in some cases.
To address this issue, a technique of crosslinking the electron transport substance is available. Japanese Patent Laid-Open No. 2003-330209 discloses addition of a polymer of an electron transport substance having a non-hydrolyzable polymerizable functional group to an undercoat layer.
Crosslinking the electron transport substance reduces the occurrence of leaching. However, crosslinking inhibits sufficient withdrawal of electrons from the photosensitive layer (charge generation layer). Thus charge accumulation may occur and insufficient sensitivity may result.